Characterization Of The Thermal Damage Of Structural Steel By Magnetic Parameters Of Barkhausen Noise And The Analysis Of Influence Factors

According to the coupling between the magnetic and mechanical properties of material, the method using the magnetic parameters to characterize the degree of thermal damage of structural steel is studied. It provides the important significance of theory and the technical using value on both fatigue life forecast and the reliability evaluate of the structural workpieces. Analyzing method combining experiment testing and theoretical calculating is used in this paper. The correlation between magnetic parameters of Barkhausen Noise (13N) and the fatigue properties is studied. Further more, the creative research conclusion is found through the all-sided analysis on the stress, strain and microstructure of materials which affect the magnetic parameters.The feasibility using the ratio of magnetic parameters of BN (namely BNr) to characterize the extent of thermal damage of 300M steel is found through the corresponding testing between the value of magnetic parameters of BN and the fatigue lifetime. It is found that BNr is non-linearly correlated with the percentage reduction of fatigue life, and is nearly linearly correlated with the percentage reduction of fatigue strength. The analysis show the residual tensile stress and the change of microstructure appear near the thermal damage area is the mechanism of the reduction of the fatigue life. The microstructure of material on the surface part of structural workpieces is changed by high temperature heat in short time, and the mechanical properties of the heated areas are reduced as well.The study results of microstructures show that the magnetic parameters of BN are certain affected by the change of microstructures caused by different process of the heat treatment. It shows that the BN amplitude is most sensitive to the high temperature tempered structure, less sensitive to the annealed structure, and least sensitive to the low temperature tempered structure and quenching structure. In the tensile stress range and on the same stress and testing conditions, the highest BN value is excited by high temperature tempered structure, the second highest BN value is excited by annealed structure, and the lowest BN value is induced by low temperature tempered structure and quenching structure.The results of four point bending tests show that the amplitude of BN signal increases when tensile stress increased, and decreases when press stress increased.